The present invention relates to an electronic device including a switch-type electronic device such as a push switch adapted to be mounted on a printed circuit board to be disposed in various kinds of electronic apparatuses.
There are known various kinds of switch-type electronic devices such as a push switch mounted on a printed circuit board of an electronic apparatus (see, Japanese Patent Publication No. 9-120742 A).
Such a push switch requires a countermeasure for preventing a static electricity carried by a hand or a finger of an operator from supplying a circuit of the electronic apparatus through an operating member of the push switch. As the countermeasure, an earth terminal for releasing the static electricity to an earth circuit of the printed circuit board is ordinarily provided in an electric conductor in the vicinity of the operating member of the electronic apparatus.
As the conventional switch-type electronic device to which the countermeasure for the static electricity is applied, one example will be described by referring to FIGS. 10 to 14.
As shown in FIG. 11, a push switch 101 comprises a box-shaped housing 102 formed with a space 103 an upper side of which is opened. A circular dome-shaped movable contact 104 made of an elastic thin metal plate is disposed on an inner bottom part of the space 103. A central lower face of the movable contact 104 opposes fixed contacts 105a and 105b each of which is made of the thin metal plate and fixed on the housing 102 by insertion molding. A protective film 106 is disposed on an upper part of the movable contact 104, and an operating member 107 made of resin is disposed on the protective film 106. A cover 108 made of metal is attached to the housing 102 so as to cover the operating member 107 from above.
The housing 102 includes engaging projections 109 respectively protruding outward along a lower face 102c of the housing 102 at right and left corners of front and rear side faces 102a and 102b of the housing 102. Further, in the other end sides, lead terminals 105A and 105B are provided that are directed outward the right and left side faces 102d and 102d of the housing 102 from the lower face 102c. 
The operating member 107 includes a pressed part 107a and an elastic actuator 107b. The pressed part 107a extends from a front side face 102a of the housing 102 through an opening 111 formed in the front side face 102a. 
The cover 108 is located on an upper face of the housing 102. The cover 108 includes an upper plate 108a having an inclined piece obliquely extended from a center part thereof toward the inside of the space 103. A pair of legs 108a are extended downward from a front edge of the upper plate 108a along the front side face 102a of the housing 102. A pair of legs 108b are extended downward from a rear edge of the upper plate 108a along a rear side face 102b. At a lower end of each of the legs 108b, an engagement piece 108c is formed so as to oppose a lower face of an associated one of the engagement projections 109. The engagement pieces 108c are bent and caulked so that the cover 108 is retained on the housing 102.
The pair of right and left legs 108b provided in the front side face 102a of the housing 102 are separated from each other sufficiently so that at least the operating member 107b of the operating member 107 can be described therebetween.
At the center of a rear end of the upper face plate 108a, an earth terminal piece 112 is provided and extended downward along the rear side face 102b of the housing 102 from the rear end of the upper face plate 108a. The lower face of the earth terminal piece 112 is substantially flush with the bottom face of the housing 102 and the lower part thereof is bent to be substantially L-shaped.
In the conventional push switch 101, as shown in FIG. 14, the operating member 107 is projected forward (leftward in FIG. 14) from a printed circuit board 115 on which the push switch is mounted and the lead terminals 105A and 105B are respectively soldered to an associated wiring pattern so that the push switch 101 is mounted on the printed circuit board. Further, when the push switch is mounted on the printed circuit board, the earth terminal piece 112 of the cover 108 is also soldered to a corresponding wiring part of an earth circuit.
In the push switch 101 mounted on the printed circuit board 115 in such a way, under a state that the operating member 107 is arranged at a position shown by a dashed chain line in FIG. 11, when a front end of the pressed part 107a is horizontally pressed rearward, the operating member 107 horizontally moves on the protecting film 106 along the upper face of the housing 102 and the end of the operating member 107b is directed downward by the inclined piece 110 to apply a push down force to the movable contact 104 located at a lower part.
When the push down force exceeds a prescribed level, as shown by a solid line of FIG. 11, the lower face of the central part of the movable contact 104 moves downward and comes into contact with the fixed contacts 105a and 105b to obtain a conductive state (turn-on state) in which the lead terminals 105A and 105B are short-circuited through the movable contact 104. As an amount of pushing operation of the operating member 107, when the rear face of the pressed part 107a abuts against the front side face 102a of the housing 102, a further pushing operation is regulated.
When the operating force of the pressed part 107a is released, the movable contact 104 is self-restored to an original attitude to push up the operating member 107b and the end of the operating member 107b is guided by the inclined piece 110, so that the operating member 107 is pushed back forward to the position shown by the dashed chain line in FIG. 11 to return to an original non-conductive state (turn-off state).
When the finger of a person who operates the push switch 101 mounted on the printed circuit board 115 of an electric apparatus in use presses the front end of the pressed part 107a, even if a static electricity carried by the body of the operator is supplied to the operating member 107 from the finger, the static electricity is supplied to an earth circuit of the printed circuit board 115 through the cover 108 and the earth terminal piece 112.
However, as in the conventional push switch, in a structure that the earth terminal piece 112 is extended downward along the rear side face 102b of the housing 102 from the rear end of the upper face plate 108a and the earth terminal piece 112 is soldered to the wiring part of the earth circuit of the printed circuit board 115 to avoid the static electricity problem, when the earth terminal piece 112 is soldered, a flux may possibly enter a clearance S1 (see FIG. 14) between the housing 102 and the earth terminal piece 112 due to a capillary phenomenon. In these days, downsizing of such a push switch is strongly demanded, and the width of each side face of the housing 112 is less than 3 mm. In such a size, the above-described capillary phenomenon becomes remarkable, and the movement of the flux is hardly controlled during soldering.
As a countermeasure for preventing the entry of the flux, a width of the clearance S1 may be increased to eliminate the capillary phenomenon. However, contrary to the above-described demand, the size of the push switch is increased in accordance with the increase of the width of the clearance S1. Further, since the end of the earth terminal piece 112 is bent outward at right angles, the size is further enlarged by such an amount S2 that the end of the earth terminal piece 112 is projected from the cover 108.
Since the earth terminal piece 112 and the lead terminals 105A, 105b are soldered to the circuit board respectively, they should be made flush with each other. However, since the earth terminal piece 112 is provided on the cover 108, an accuracy of height of the earth terminal piece 112 to the circuit board depends on an accuracy of assembling the cover 108 to the housing 102. Thus, a height difference with respect to the circuit board among the earth terminal piece 112 and the lead terminals 105A, 105B is hardly to be avoided. In other words, it is difficult to obtain the coplanarity among the earth terminal piece 112 and the lead terminals 105A, 105B, especially in a case where a thin metal mask for soldering is used to attain the height reduction.